Chapter 14: Local Area Network Technology Business Data Communications, 4e

PC Networks 8Client/Server Communication 8Shared databases 8Shared hardware resources 8Shared Internet access 8Peer-to-Peer Communication 8Sharing work and information with colleagues 8Low cost is high priority 8Attachment costs in the hundreds of dollars

Backend & Storage Area Networks 8“Computer room networks” 8Interconnect large systems (mainframes, supercomputers, etc) 8Key requirement is high-speed bulk transfer 8Usually limited distance, few drops 8Speed more important than cost 8Attachment costs in the thousands of dollars

High-Speed Office Networks 8Increased processing and transfer requirements in many graphics-intensive applications now require significantly higher transfer rates 8Decreased cost of storage space leads to program and file bloat, increased need for transfer capacity 8Typical office LAN runs at 1-20mbps, high- speed alternatives run at 100+

Backbone Local Networks 8Used instead of single-LAN strategy 8Better reliability 8Higher capacity 8Lower cost

Factory Networks 8High capacity 8Ability to handle a variety of data traffic 8Large geographic extent 8High reliability 8Ability to specify and control transmission delays

Tiered LANs 8Cost of attachment to a LAN tends to increase with data rate 8Alternative to connecting all devices is to have multiple tiers 8Multiple advantages 8Higher reliability 8Greater capacity (less saturation) 8Better distribution of costs based on need

Tiered LAN Strategies 8Bottom-up strategy: individual departments create LANs independently, eventually a backbone brings them together 8Top-down strategy: management develops an organization-wide networking plan

Tiered LAN Diagram

LAN Topology 8Arrangement of workstations in a shared medium environment 8Logical arrangement (data flow) 8Physical arrangement (cabling scheme)

LAN Topologies: Bus 8Multipoint medium 8Stations attach to linear medium (bus) using tap 8Full-duplex between station and tap 8Transmission from any stations travels entire medium (both directions) 8Termination required at ends of bus

Bus LAN Diagram

LAN Topologies: Tree 8Generalization of bus topology 8Branching cable with no closed loops 8Cable(s) begin at headend, travel to branches which may have branches of their own 8Each transmission propagates through network, can be received by any station

Tree LAN Diagram

Bus/Tree Topology Problems 8How do you identify who the transmission is intended for? 8Data transmitted in frames 8Each frame has header with addressing info 8How do you regulate access? 8Stations take turns sending, by monitoring control information in frames

LAN Topologies: Ring 8Repeaters are joined by unidirectional point- to-point links in a ring 8As a frame circulates past a receiver, the receiver checks its address, and copies those intended for it into a local buffer 8Frame circulates until it returns to source, which removes it from network

Ring LAN Diagram

LAN Topologies: Star 8Each station connected directly to central node, usually with two undirectional links 8Central node can broadcast info, or can switch frames among stations

Star LAN Diagram

Choosing a Topology 8Factors to consider include reliability, flexibility/expandability, and performance 8Bus/tree is most flexible 8Tree topology easy to lay out 8Ring provides high througput, but reliability problems 8Star can be high speed for short distances, but has limited expandability

Transmission Media Options 8Twisted pair--digital signaling 8Optical fiber--analog signaling 8Baseband coax--digital signaling 8Broadband coax--analog signaling 8Uses FDM to carry multiple channels 8Can be used over longer distances 8Inherently unidirectional, due to amplifier limitations

Selecting Transmission Media 8Capacity: Can it support expected network traffic? 8Reliability: Can it meet requirements for availability? 8Types of data supported: Is it well-suited to the applications involved? 8Environmental scope: Can it provide service in the environments required?

Medium and Topology

Structured Cabling System 8Standards for cabling within a building (EIA/TIA- 568 and ISO 11801) 8Includes cabling for all applications, including LANs, voice, video, etc 8Vendor and equipment independent 8Designed to encompass entire building, so that equipment can be easily relocated 8Provides guidance for pre-installation in new buildings and renovations

Wiring Layouts 8Wiring layout is different from logical topology 8Linear layout minimizes amount of cable 8Star layout uses individual cable from concentration point to subscribers 8Can be used for bus and ring as well as star 8Concentration point can be wiring closet or hub (an active node that accepts frames and regenerates signals for transmission)

LAN Standards (802.x) 8Advantages of standards 8Assure sufficient volume to keep costs down 8Enable equipment from various sources to interconnect 8IEEE 802 committee developed, revises, and extends standards 8Use a three-layer protocol hierarchy: physical, medium access control (MAC), and logical link control (LLC)

Logical Link Control 8Specifies method of addressing and controls exchange of data 8Independent of topology, medium, and medium access control 8Unacknowledged connectionless service (higher layers handle error/flow control, or simple apps) 8Connection-mode service (devices without higher- level software) 8Acknowledged connectionless service (no prior connection necessary)

Medium Access Control 8Provides a means of controlling access to a shared medium 8Two techniques in wide use 8CSMA/CD 8Token passing 8LLC frames data, passes it to MAC which frames it again 8MAC control (e.g. priority level) 8Destination physical address 8Source physical address

Bridges 8Allow connections between LANs and to WANs 8Operates at Layer 2 (Data Link Layer) of OSI 8Used between networks using identical physical and link layer protocols 8Provide a number of advantages 8Reliability: Creates self-contained units 8Performance: Less contention 8Security: Not all data broadcast to all users 8Geography: Allows long-distance links

Bridge Functions 8Read all frames from each network 8Accept frames from sender on one network that are addressed to a receiver on the other network 8Retransmit frames from sender using MAC protocol for receiver 8Must have some routing information stored in order to know which frames to pass

Bridge Operation

Hubs 8The active central element of the star layout. 8When a single station transmits, the hub repeats the signal on the outgoing line to each station. 8Physically a star; logically a bus. 8Hubs can be cascaded in a hierarchical configuration.

Two-Level Star Topology

Layer 2 Switches (Switching Hubs)

Ethernet Hubs and Switches 8Shared medium hubs 8Switched LAN hubs x

Advantages of Switched Hubs 8No modifications needed to workstations when replacing shared-medium hub 8Each device has a dedicated capacity equivalent to entire LAN 8Easy to attach additional devices to the network

Types of Switched Hubs 8Store and forward switch 8Accepts a frame on input line 8Buffers it briefly 8Routes it to appropriate output line 8Cut-through switch 8Begins repeating the frame as soon as it recognizes the destination MAC address 8Higher throughput, increased chance of error

Layer 3 Switches 8Problems With Layer 2 Switches 8Broadcast overload 8Lack of multiple links 8Can be solved with subnetworks connected by routers 8Layer 3 switches implement the packet- forwarding logic of the router in hardware.